Checkpoint Inhibition In Pediatric Hepatocellular Carcinoma

This study is testing an immunotherapy drug called pembrolizumab (a checkpoint inhibitor that helps the immune system fight cancer) in children and young adults with liver cancer (hepatocellular carcinoma or HCC) that has come back or has not responded to prior treatments. **You may be eligible if...** - You are under 30 years old - You have been diagnosed with relapsed or treatment-resistant hepatocellular carcinoma (liver cancer), confirmed by biopsy - Your cancer is measurable on imaging - Your general health performance level is adequate (Karnofsky or Lansky ≥ 60%) - Your blood counts and organ function (liver, kidney) are within acceptable levels - You agree to use contraception during and for 4 months after treatment **You may NOT be eligible if...** - You have previously received a checkpoint inhibitor (PD-1, PD-L1, or CTLA-4 inhibitor) - You are on chronic steroids or immunosuppressive medications - You have HIV, a known autoimmune disease (other than childhood asthma or eczema), or had an organ transplant - You are currently pregnant Talk to your doctor to see if this trial is right for you.